1. Field of the Invention
The present invention relates to a surface light source device, and more specifically to a surface light device which is applied to a mobile terminal such as a PDA (Personal Digital Assistants), for example.
2. Description of the Prior Art
One example of such a Kind of a surface light source device is disclosed in, for example, Japanese Patent Laying-open No. 10-153778 [G02F 1/1335, F21V 8/00, G02B 6/00] laid-open on Jun. 9, 1998. As shown in FIG. 8 an entire part of this side-light type surface light source device 1 was maintained by a frame 2. The frame 2 was formed in such a manner that an edge of a side of an emitting surface 3a is protruded by a predetermined length L from an incidence surface 3b side of a light scattering and guiding plate 3, and therefore, an illumination light which is incident onto a lower edge 3c of a side of an incidence surface 3b on the light scattering and guiding plate 3 and directly emitted from an emitting surface 3a is shielded by a light emitted from a lam light source 4. Thus a bright line is prevented from being formed in the vicinity of the lamp light source 4 on the emitting surface 3a. 
However, in this prior art, due to a fact that the frame 2 was formed in such a manner that an edge of a side of an emitting surface 3a is protruded by a predetermined length L from the incidence surface 3b side of the light scattering and guiding plate 3, the illumination light was shielded, and therefore, the emitting surface 3a becomes narrower.
Therefore, it is a primary object of the present invention to provide a surface light source device capable of preventing a bright line and securing an emitting surface to the fullest extent.
A surface light source device according to the present invention, comprises: a linear light source which emits a linear light; a light guide plate having one side surface to which an emitted light from the linear light source is incident and an upper surface from which the light is emitted; a translucent member which is arranged as to cover the upper surface of the light guide plate and has a first area of a first translucent rate and a second area of a second translucent rate higher than the first translucent rate; and a light-shielding member which is inserted between the light guide plate and the translucent member and shields a portion of the light emitted from the upper surface of the light guide plate; a light-shielding effect of the shielding member being decreased with distance from the one side surface.
In the surface light source device according to the present invention, a light emitted from the linear light source of a linear shape is incident onto the one side surface of the light guide plate, and in turn, emitted from the upper surface of the light guide plate. A translucent member is provided so as to cover such the light guide plate, and the translucent member has a first area of a first translucent rate and a second area of a second translucent rate higher than the first translucent rate. Furthermore, between the light guide plate and the translucent member, a shielding member is provided to intercept (shield) the light emitted from the light guide plate. The first area is arranged to be closer to the one side surface side of the light guide plate from the second area, i.e. on the linear light source side, and the light-shielding effect of the light-shielding member is decreased with a direction toward the second area from the first area. Therefore, because most of the light which is emitted from the light guide plate and exposing the first area is shielded by the light-shielding member, it is thus possible to prevent from suddenly increasing a luminance or intensity in the vicinity of the linear light source. That is, it is possible to make the light emitted from the second area almost equal.
According to the present invention, because it is possible to prevent from abruptly increasing the luminance in the vicinity of the linear light source by providing the light-shielding member having a light-shielding effect that is continuously varied, a bright line is never formed in the second area. Furthermore, due to a fact that a light can be emitted in the vicinity of the linear light source such as the second area, it is possible to secure the emitting surface to the fullest extent.
In one aspect of the present invention, if and when a negative image formed of a material having the first translucent rate is printed on the first translucent member, it is possible to illuminate the negative image by the light emitted via the light-shielding member.
In one embodiment of the present invention, it is possible to display a color image in the second area because a reflection type liquid crystal panel is arranged at a lower surface of the light guide plate to be opposed to the second area.
In another embodiment of the present invention, if a diffusing member is provided to diffuse a light between the translucent member and the light-shielding member, it is possible to make the light emitted from the second area even more equal. It is noted that the same effect is obtained by providing the diffusing member between the light guide plate and the light-shielding member.
The above described objects and other objects, features, aspects and advantages of the present invention will become more apparent from the following detailed description of the present invention when taken in conjunction with the accompanying drawings.